The DNA sequence (GA)n.(CT)n has been found to slow fork progression in monkey cells. It is suggested that this sequence may therefore play an important role in gene amplification. Several of the sequences we previously isolated as potential origins of replication have been shown to stimulate plasmid replication in transfection experiments. We have been investigating one of these sequences intensively because it is a member of a moderately reiterated sequence, often found in tandem in an arrangement reminiscent of bacterial transposons. We have identified a portion of this "0-family" sequence which is site specifically protected by a protein present in cell extracts. We are currently attempting to demonstrate transposon-like activity for this sequence.